1. Field of the Invention
The present invention relates to endoscopic irrigation instruments. More particularly, the present invention relates to a tapered irrigation tube which permits an endoscopic irrigation instrument to be used with irrigation sources of different pressures.
2. State of the Art
Endoscopic suction-irrigation instruments are used for supplying suction and irrigation to a surgical site during endoscopic surgery. Irrigation fluid is introduced to the surgical site through an irrigation tube to rinse away blood and other matter. Suction applied through a suction tube removes the fluid with the waste. In the past, many incisions were made during surgery to allow insertion of separate suction and irrigation tubes as well as the endoscopic instruments used in the surgery. Recently, in order to reduce the number of incisions in the body, single instruments have been utilized incorporating both irrigation and suction.
Instruments which incorporate both suction and irrigation are typically connected by flexible tubes to separate suction and irrigation sources. Parent application, Ser. No. 07/959,280 discloses an endoscopic electrosurgical suction-irrigation instrument having a cannula fitted in a fluid chamber, with suction and irrigation tubes coupled to the chamber. Pinch valves coupled to triggers are used to control the flow of fluid through the tubes.
There are various constraints on the design of an endoscopic irrigation instrument. For example, the irrigation supply tube must be constructed to be strong enough to contain fluid located therein which may be pressurized to different pressures when the supply tube is pinched off, but also thin and flexible enough to allow a pinch valve in the instrument to pinch off the flow of fluid through the tube. At the same time it is desirable to provide a tube which enables as large a fluid flow stream as possible in the endoscopic irrigation instrument. These conflicting requirements must be balanced. The irrigation system in the parent application balances these requirements by providing an irrigation tube with a small diameter which is coupled at one end to the fluid chamber and on the other end to a connector inside the instrument, and a second tube of a larger diameter at the outside of the instrument which is coupled to the other side of the connector and to the irrigation source. The small irrigation tube at the inside of the instrument permits the pinch valve to stop the flow of the fluid through the tube when desired. The large diameter irrigation tube at the outside of the instrument allows more flow from the irrigation source to the instrument.
A disadvantage of the arrangement of the instrument disclosed in parent application is that when a high pressure fluid source is applied through the irrigation tube, the connector between the smaller and larger diameter tube can leak, and/or the tubes disconnect. A possible solution to this problem is to use a single thin tube from the irrigation source up to the fluid chamber of the endoscopic irrigation instrument. However, with the smaller diameter tube there would be less flow from the source than if the larger diameter tube were used.